Income Taxes - Temporary Differences and Carryforwards Giving Rise to Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deferred income tax asset (liability):
Federal and state net operating loss (NOL) carryforwards	$ 398	$ 601
Deferred revenue	1,232	1,090
Employee benefits, including pension, postretirement and medical	885	1,051
Other	408	351
Less: Valuation allowance	(59)	(63)
Total deferred tax assets	2,864	3,030
Depreciation	(2,929)	(2,431)
Intangibles	(749)	(803)
Total deferred tax liabilities	(3,678)	(3,234)
Net deferred tax liability	(814)	(204)
United Airlines, Inc.
Deferred income tax asset (liability):
Federal and state net operating loss (NOL) carryforwards	372	574
Deferred revenue	1,232	1,090
Employee benefits, including pension, postretirement and medical	885	1,051
Other	406	351
Less: Valuation allowance	(59)	(63)
Total deferred tax assets	2,836	3,003
Depreciation	(2,929)	(2,431)
Intangibles	(749)	(803)
Total deferred tax liabilities	(3,678)	(3,234)
Net deferred tax liability	$ (842)	$ (231)